This invention relates to alumina-bearing ores such as bauxite, and more particularly, it relates to a process for treating alumina-bearing ores to recover the metal values therein.
The Bayer process is used for recovering substantially pure alumina from bauxite and uses NaOH to dissolve the alumina in the bauxite. Most of the other components of the bauxite are inert in the process, except silica, some of which reacts with the hydroxide. The inert components and the silica and silica compounds are rejected and are referred to as red mud or red sludge. This waste product from the Bayer process has presented serious disposal problems. Red mud can contain 11 to 45 wt. % Al2O3, 5 to 66 wt. % Fe2O3, 1 to 16 wt. % SiO2, 6 to 17 wt. % TiO2 and 3 to 8 wt. % Na2O.
Many attempts have been made to recover the metal values from red mud. For example, U.S. Pat. No. 3,574,537 discloses a process for the treatment of red-mud to extract Fe2O3, Al2O3, SiO2 and Na2O, in which SO2 is passed into a solution of red-mud and the Fe2O3 separated therefrom. The liquor is heated until a pH of 4.5 to 5.0 is reached forming a precipitate of SiO2 and Al(OH)SO3. The precipitate is separated from the liquor which is concentrated to crystallize out Na2SO3. Sulphuric acid is added to the separated precipitate forming water-soluble aluminum salts. SiO2 remains as a residue and is removed from solution. Water and a potassium or ammonium salt is added to the liquor from which the corresponding alum may be crystallized out.
U.S. Pat. No. 4,119,698 discloses that red mud is digested with concentrated sulfuric acid or with sulfur trioxide gas to produce sulfates that can be leached out to the resulting mass with water. The solution is then heated at a pH of 1 to precipitate titanium oxide hydrate by hydrolysis. The remaining sulfates of the solution are then obtained in solid form by evaporation, or by precipitation with acetone, and the solid is then roasted to convert the aluminum and iron to the oxide. After leaching out the sodium sulfate with water, the aluminum and iron oxide are separated by the Bayer process, which works in this case even though x-ray diffusion patterns show that the aluminum oxide is mainly xcex1Al2O3.
U.S. Pat. No. 4,017,425 discloses a method for activating the red mud formed in the Bayer alumina producing process for allowing its use as adsorbent, catalyst, ion-exchanging substance and clarifying substance, comprising digesting red mud and dispersing the metal oxide compound particles in the compound of metal hydroxides and silica gel.
U.S. Pat. No. 5,043,077 discloses a method of treating Bayer process red mud slurries to improve or facilitate the handling thereof, comprising adding to such a slurry a minor proportion of humic acids or humates effective to reduce the viscosity of the slurry.
Australian patent 223,794 discloses treating red mud by first calcining then forming a slag in an electric furnace followed by treating the slag with sulfuric acid. Alumina can be recovered from aluminum sulfate by heating.
German Patent 26 53 762 discloses a treatment for red mud which comprises heating to 250xc2x0 to 350xc2x0 C. (pref 280xc2x0 to 320xc2x0 C.), adding concentrated H2SO4 or S03 gas, leaching the sulphates formed with water and separating the solution. Ti oxide is precipitated after adjusting the pH to 1 and the solid Ti oxide is separated by filtering. Acetone is added or the solution is evaporated to crystallize the sulphates which are roasted at 900 to 1000xc2x0 C. The remaining Na sulphate is leached with water and the oxides of Al and Fe remaining are treated by the Bayer process.
Japanese reference JP54137-499 discloses that silica, titania and alumina can be separated from red mud by adding sulfuric acid and then ammonia, reducing trivalent iron to divalent, and hydrolyzing by adjusting pH.
It will be seen from the above that great effort is expended to recover the values from red mud. Thus, there is still a great need for a process which can extract the metal values from alumina-bearing ores in an economical manner which does not generate red mud. The instant invention provides such a process.
It is an object of the present invention to provide a process to recover metal values from alumina-bearing ores.
It is another object of the present invention to provide a process for recovering alumina, iron oxide, silica and titania values from alumina-bearing ores.
It is a further object of the present invention to provide an acid process for recovering the metal values from alumina-bearing ores.
It is still a further object of the present invention to provide an acid digesting process for recovering the metal values from alumina-bearing ores in an economical manner.
These and other objects will become apparent from a reading of the specification and claims appended hereto.
In accordance with these objects, there is provided a method for processing alumina-bearing ores to recover iron, aluminum, silicon and titanium metal values therefrom, the method comprising the steps of adding the alumina-bearing ores to a digester containing an acid to provide a mixture of acid and alumina-bearing ores and heating the mixture to dissolve soluble compounds of at least one of iron, aluminum, silicon and titanium to provide a digest containing dissolved salts of the soluble compounds and to provide a gas component. Thereafter, the digest is treated with water to dissolve water soluble salts therein to provide a slurry comprised of a liquid containing water and the dissolved soluble salts and a solid component comprised of silica. The solid component is separated from the liquid and the pH of the liquid is adjusted to form an iron-containing precipitate. The iron-containing precipitate is separated from the liquid to provide an iron-depleted liquid whose pH is adjusted to precipitate aluminum trihydrate which is separated from the iron-depleted liquid to provide an aluminum trihydrate-depleted liquid. The pH of the aluminum trihydrate-depleted liquid may be adjusted to form a precipitate comprised of at least one remaining salt in the aluminum trihydrate-depleted liquid to provide a salt-depleted liquid. The salt precipitate is separated from the salt-depleted liquid thereby recovering the metal values from the alumina-bearing ores.